1,136 research outputs found

    Entanglement vs. gap for one-dimensional spin systems

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    We study the relationship between entanglement and spectral gap for local Hamiltonians in one dimension. The area law for a one-dimensional system states that for the ground state, the entanglement of any interval is upper-bounded by a constant independent of the size of the interval. However, the possible dependence of the upper bound on the spectral gap Delta is not known, as the best known general upper bound is asymptotically much larger than the largest possible entropy of any model system previously constructed for small Delta. To help resolve this asymptotic behavior, we construct a family of one-dimensional local systems for which some intervals have entanglement entropy which is polynomial in 1/Delta, whereas previously studied systems, such as free fermion systems or systems described by conformal field theory, had the entropy of all intervals bounded by a constant times log(1/Delta).Comment: 16 pages. v2 is final published version with slight clarification

    Online Independent Set Beyond the Worst-Case: Secretaries, Prophets, and Periods

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    We investigate online algorithms for maximum (weight) independent set on graph classes with bounded inductive independence number like, e.g., interval and disk graphs with applications to, e.g., task scheduling and spectrum allocation. In the online setting, it is assumed that nodes of an unknown graph arrive one by one over time. An online algorithm has to decide whether an arriving node should be included into the independent set. Unfortunately, this natural and practically relevant online problem cannot be studied in a meaningful way within a classical competitive analysis as the competitive ratio on worst-case input sequences is lower bounded by Ω(n)\Omega(n). As a worst-case analysis is pointless, we study online independent set in a stochastic analysis. Instead of focussing on a particular stochastic input model, we present a generic sampling approach that enables us to devise online algorithms achieving performance guarantees for a variety of input models. In particular, our analysis covers stochastic input models like the secretary model, in which an adversarial graph is presented in random order, and the prophet-inequality model, in which a randomly generated graph is presented in adversarial order. Our sampling approach bridges thus between stochastic input models of quite different nature. In addition, we show that our approach can be applied to a practically motivated admission control setting. Our sampling approach yields an online algorithm for maximum independent set with competitive ratio O(ρ2)O(\rho^2) with respect to all of the mentioned stochastic input models. for graph classes with inductive independence number ρ\rho. The approach can be extended towards maximum-weight independent set by losing only a factor of O(logn)O(\log n) in the competitive ratio with nn denoting the (expected) number of nodes

    Molecular Diagnosis of Human Papillomavirus: Comparison Between Cervical and Vaginal Sampling

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    Background: Human papillomavirus (HPV) is the most significant cause of cervical cancer. In view of the number of drawbacks associated with endocervical sampling, the gold standard for HPV detection, this study examined the utility and specificity of vaginal sampling as an alternative for endocervical sampling for the routine detection of HPV. Case study: The study comprised 51 women who tested positive and 54 women who tested negative for endocervical HPV by polymerase chain reaction (PCR), confirmed by histopathology. At the time of specimen collection, both (speculum-assisted) endocervical and vaginal (no speculum) scrapings were isolated from HPV positive and negativewomen, and HPV DNA was assessed by PCR using the MY09/MY11 primer system;HPV type was identified by hybridization of PCR products with type-specific biotinylated DNA probes. Each participant served as her own control. HPV was detected in vaginal and cervical scrapes from all HPV-positive but not HPV-negative women. In HPV-positive women the same HPV type was found in vaginal and endocervical scrapings (positive predictive value = 1.0). Conclusion: Correlation between vaginal and endocervical sampling methods was excellent in detecting the presence of HPV DNA and for identifying distinct HPV genotypes. Utilization of vaginal testing for routine HPV detection, and for the long-term follow-up of persistent HPV infection, is therefore recommended

    The role of e-participation and open data in evidence-based policy decision making in local government

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    The relationships between policies, their values and outcomes are often difficult for citizens and policy makers to assess due to the complex nature of the policy lifecycle. With the opening of data by public administrations there is now a greater opportunity for transparency, accountability and evidence-based decision making in the policy making process. In representative democracies, citizens rely on their elected representatives and local administrations to take policy decisions that address societal challenges and add value to their local communities. Citizens now have the opportunity to assess the impact and values of the policies introduced by their elected representatives and hold them accountable by utilising historical open data that is publicly available. Using a qualitative case study in a UK Local Government Authority, this paper examines how e-participation platforms and the use of open data can facilitate more factual, evidence based and transparent policy decision making and evaluation. From a theoretical stance, this paper contributes to the policy lifecycle and e-participation literature. The paper also offers valuable insights to public administrations on how open data can be utilised for evidence-based policy decision making and evaluationThis work evolved in the context of the project Policy Compass (http://policycompass.eu/), a project co-funded by the EC within FP7, Grant agreement no: 612133

    Wear Minimization for Cuckoo Hashing: How Not to Throw a Lot of Eggs into One Basket

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    We study wear-leveling techniques for cuckoo hashing, showing that it is possible to achieve a memory wear bound of loglogn+O(1)\log\log n+O(1) after the insertion of nn items into a table of size CnCn for a suitable constant CC using cuckoo hashing. Moreover, we study our cuckoo hashing method empirically, showing that it significantly improves on the memory wear performance for classic cuckoo hashing and linear probing in practice.Comment: 13 pages, 1 table, 7 figures; to appear at the 13th Symposium on Experimental Algorithms (SEA 2014

    Nature of Nitrogen Incorporation in BiVO4 Photoanodes through Chemical and Physical Methods

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    In recent years, BiVO4 has been optimized as a photoanode material to produce photocurrent densities close to its theoretical maximum under AM1.5 solar illumination. Its performance is, therefore, limited by its 2.4 eV bandgap. Herein, nitrogen is incorporated into BiVO4 to shift the valence band position to higher energies and thereby decreases the bandgap. Two different approaches are investigated: modification of the precursors for the spray pyrolysis recipe and post-deposition nitrogen ion implantation. Both methods result in a slight red shift of the BiVO4 bandgap and optical absorption onset. Although previous reports on N-modified BiVO4 assumed individual nitrogen atoms to substitute for oxygen, X-ray photoelectron spectroscopy on the samples reveals the presence of molecular nitrogen (i.e., N-2). Density functional theory calculations confirm the thermodynamic stability of the incorporation and reveal that N-2 coordinates to two vanadium atoms in a bridging configuration. Unfortunately, nitrogen incorporation also results in the formation of a localized state of approximate to 0.1 eV below the conduction band minimum of BiVO4, which suppresses the photoactivity at longer wavelengths. These findings provide important new insights on the nature of nitrogen incorporation into BiVO4 and illustrate the need to find alternative lower-bandgap absorber materials for photoelectrochemical energy conversion applications

    Space-time super-resolution

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    Camera motion estimation through planar deformation determination

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    In this paper, we propose a global method for estimating the motion of a camera which films a static scene. Our approach is direct, fast and robust, and deals with adjacent frames of a sequence. It is based on a quadratic approximation of the deformation between two images, in the case of a scene with constant depth in the camera coordinate system. This condition is very restrictive but we show that provided translation and depth inverse variations are small enough, the error on optical flow involved by the approximation of depths by a constant is small. In this context, we propose a new model of camera motion, that allows to separate the image deformation in a similarity and a ``purely'' projective application, due to change of optical axis direction. This model leads to a quadratic approximation of image deformation that we estimate with an M-estimator; we can immediatly deduce camera motion parameters.Comment: 21 pages, version modifi\'ee accept\'e le 20 mars 200

    A chemiluminescent method for the detection of H 2 O 2 and glucose based on intrinsic peroxidase-like activity of WS 2 quantum dots

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    Currently, researchers are looking for nanomaterials with peroxidase-like activity to replace natural peroxidase enzymes. For this purpose, WS 2 quantum dots (WS 2 QDs) were synthesized via a solvothermal method, which improved the mimetic behavior. The resulting WS 2 QDs with a size of 1�1.5 nm had a high fluorescence emission, dependent on the excitation wavelength. WS 2 QDs with uniform morphology showed a high catalytic effect in destroying H 2 O 2 . The peroxidase-like activity of synthesized nanostructures was studied in H 2 O 2 chemical and electrochemical reduction systems. The mimetic effect of WS 2 QDs was also shown in an H 2 O 2 �rhodamine B (RB) chemiluminescence system. For this aim, a stopped-flow chemiluminescence (CL) detection system was applied. Also, in order to confirm the peroxidase-like effect of quantum dots, colorimetry and electrochemical techniques were used. In the enzymatic reaction of glucose, H 2 O 2 is one of the products which can be determined. Under optimum conditions, H 2 O 2 can be detected in the concentration range of 0�1000 nmol·L � 1 , with a detection limit of 2.4 nmol·L � 1 . Using this CL assay, a linear relationship was obtained between the intensity of the CL emission and glucose concentration in the range of 0.01�30 nmol·L � 1 , with a limit of detection (3S) of 4.2 nmol·L � 1 © 2019 by the authors
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